1. Field of the Invention
The invention relates to an electric vehicle, and in particular to an electric vehicle including a transmission, and a converter that regulates voltage supplied to a drive unit that drives an electric motor.
2. Description of Related Art
A motor drive control system including a motor, an inverter, and a converter that regulates the input voltage of the inverter is disclosed in International Publication No. 2003/015254. In the motor drive control system, the optimum voltage to be applied to the motor at the moment is calculated, based on the rotational speed and target output torque (torque command) of the motor, and a target value of the inverter input voltage is determined based on the optimum voltage to be applied. With the motor drive control system thus configured, the inverter input voltage can be optimized according to operating conditions of the motor, and the motor can be efficiently driven (see WO 03/015254 A1).
When a transmission is provided in a power transmission path between a rotary shaft of the electric motor and drive wheels, the operating point (rotational speed and torque) of the electric motor can rapidly change due to shifting (change of the speed ratio) of the transmission. In the motor drive control system described in WO 03/015254 A1, the target value of the inverter input voltage is determined based on the operating point of the electric motor; therefore, the inverter input voltage may not be able to follow rapid changes in the operating point of the electric motor. As a result, the electric motor may be temporarily unable to produce desired torque, and the driveability may deteriorate.